Conventionally, there have been inkjet printers in which a piezoelectric element is used for a drive element in the printhead. In such a printhead, a voltage is applied to the piezoelectric element which deforms in response, thereby pressurizing ink contained in an ink channel. The pressurized ink is ejected in the form of an ink drop toward a recording sheet from a nozzle which is provided corresponding to the ink channel. Further, by varying the diameters of the ink drops, a gradation of printing densities can be expressed.
Currently, there is under development a printhead for ejecting an ink drop which produces an ink spot whose diameter is within a range of about 35 .mu.m to 120 .mu.m after adhering to the recording sheet. This kind of printhead can express a greater number of gradation levels by forming ink drops having a wide range of dot diameters.
However, a problem occurs with a printhead which ejects ink drops of a plurality of diameters when printing large diameter drops. If the applied voltage for driving the piezoelectric element is increased in an attempt at forming an ink drop having a relatively large diameter, then anomalies with the printed drop tend to occur which are known variously as break, curve, and satellite of ink drops.
FIGS. 6(a)-(c) show views for explaining the drop break and satellite of the ink drops. FIG. 6(a) shows an ink drop which is propelled in a normal shape. FIG. 6(b) shows an ink drop propelled with a drop break. FIG. 6(c) shows an ink drop propelled with a satellite.
The break, satellite and other anomalies of the ejected drop cause an image defect which significantly impairs the image quality.
The present invention has been developed for solving the problems as described above, and its object is to provide an inkjet recording apparatus capable of preventing the occurrence of the image defect.